This invention relates to aluminum substrates for rigid magnetic memory disks.
Aluminum alloys have been extensively used in the manufacture of rigid computer memory disks due to their high strength, light weight, low cost and good surface finishing characteristics. The aluminum alloys are used as substrates for the magnetizable layers, and are given a high yield strength by the inclusion of magnesium as an alloying component, high yield strength being one of the essential characteristics of a successful high quality memory disk.
Advances in memory storage technology such as a reduction of the thickness of the magnetizable layer and an increase in the density of information stored in it have brought changes in the requirements for disk substrates. In particular, the smoothness of the substrate has become more critical while the requirement of high yield strength still remains.
Coated and layered substrates have been disclosed in a number of U.S. patents. Peters et al., U.S. Pat. No. 3,466,156 (Sept. 9, 1969) disclose a substrate coated first with a zinc layer followed by a nonmagnetic nickel layer. Yanagisawa et al., U.S. Pat. No. 4,069,360 (Jan. 17, 1978) disclose a memory disk with an nonmagnetic nickel-phosphorus alloy layer interposed between the substrate and the magnetic layer. Nakagawa et al., U.S. Pat. No. 4,430,387 (Feb. 7, 1984) disclose the application to a substrate of a thin metal film which is readily anodized.